The processing of material by laser radiation is known. A particular application for processing transparent materials, where a processing effect is obtained by a non-linear interaction of the laser radiation with the per se transparent material, is refractive ophthalmic surgery. For surgery, the laser radiation is focused into the eye's cornea, and the focus is shifted along a cut surface to be generated.
Of course, the processing time depends on how long the interaction in the focus lasts. An acceleration can be achieved by working with several focus spots at a time.
Therefore, EP 1279386 A1, which discloses an apparatus of the above type, describes how to shorten the treatment time by multiplying the spots, allowing the simultaneous processing of larger partial areas. The presented solution has several disadvantages. According to FIG. 4 of this publication, a beam 38 is split into partial beams 44 a . . . c by lenses 42 a . . . c. The diameter the beams 44 a . . . c have directly at the lenses 42 a . . . c is smaller than the diameter of the beam 38. This is a disadvantage, because a smaller beam cross section at the lenses 42 a . . . c causes the beams 44 a . . . c to be have an inferior focusing ability as compared to the beam 38. That is, either larger spots result or the cross sections have to be adapted. After interaction of the near-parallel beam 38 with the lenses 42 a . . . c, convergent beams 44 a . . . c form so that foci are located within the optical system. This is disadvantageous because it may cause high field strengths with undesired effects within the optical system, for example an energy-consuming optical breakthrough at a position in the optical beam path other than the target position in the material to be treated. Moreover, any focusing element always generates a need for adaptation to the subsequent optics, e.g. by collimation. This accordingly results in additional complexity.
Also, in the state of the art, a scanning element is positioned directly in the intermediate image, i.e. conjugated to the actual processing plane. Although the beams would be deflected when using a galvanometer scanner, there would be no change of location. Therefore, the spots would rest in the processing volume despite any deflections of the galvanometer scanner. Further, the design according to DE 60208968 additionally uses an active mirror having 40,000 active facets, which is complex and expensive.
A further problem of the known arrangement is that a fixed offset between the individual spots is generated anterior to the scanner. A spiral scan will then result in points of intersection between the spot paths in the processing volume. This leads to a non-concentric course of the paths, especially for a small number of spots.